Last night in Illinois we had 28 degrees for 5 hours. I covered everything that I could with everything that I could find (I'm talking big garden here) but it was too windy to keep the large hydrangea covered. Since we had mid 70 degree weather for 4-5 weeks the endless summer hydrangea was nearly fully leafed out. This morning I found 50% of the leaves were black and shrunken. I don't think it had yet produced any flower buds but it is in sad shape. Many trees and bushes also suffered damage. Do leaves regrow or will I be looking at an unsightly bush all summer. Will this also mean fewer blooms this year?
Damaged leaves will eventually die, dry out and be replaced. You can cut them if you wish although I sometimes leave them if they are not too many. Then I prune them in a month if I find that they are dead. The roots should not have been affected so the shrub should recover. However, it may take some time for new growth to appear so do not despair. Keep them well mulched with 3-4" and keep the soil evenly moist. Do not apply fertilizers now because the shrub is stressed.
Damage to flower buds is more difficult to determine because you usually cannot see them. The flower buds normally occur near the end of the stems so some probably got zapped. It will mean fewer blooms from the crop of blooms that you normally get this time of the year. However, this is rebloomer ES we are talking about so, ES should generate more new flower buds around June-ish again.
Winter protection, applied in the Fall, might help alleviate some of these problems. If you decide to add protection, remove it about 1-2 weeks after your average date of last frost in Spring (your local nurseries can tell you when this is).